1. Field of the Invention
The present invention relates generally to an atomic force microscope, and more particularly to a flat-cantilever stylus for use in the atomic force microscope and a method of making the stylus. A tip of one of two principal surfaces of a cantilever is used as the stylus.
2. Description of the Prior Art
Conventionally, a scanning tunneling microscope (hereinafter referred to as STM) has been developed as an instrument capable of observing the surface of a solid body on the order of atoms. However, since the STM detects a tunnel current between a sample and a stylus to observe the sample surface, it is impossible for the STM to observe the surface of an insulator. In order to solve this problem, an atomic force microscope (hereinafter referred to as AFM) for observing the sample surface by detecting forces acting between the sample and the stylus has been proposed. Similar to the STM, the resolution of the AFM depends greatly upon the radius of curvature of the tip of the stylus. The smaller the radius of curvature is, the higher is the resolution. In order to detect minute forces, the AFM requires a cantilever 25 having a stylus 26 formed on the tip thereof, as shown in FIG. 1. In some conventional AFMs, the tip of the cantilever is used as the stylus. A cantilever with an integrated pyramidal tip can be formed by using an etch pit as a mold. The stylus may be made by anisotropic etching. In recent years, styli having a radius of curvature of approximately 300 .ANG. at the tip thereof have been obtained.
Although the AFM styli are made by various methods as described above, each method has a problem or problems. When the tip of the cantilever is utilized as the stylus, there are no problems in connection with adhesive properties between the cantilever and the stylus, and the manufacturing processes are comparatively simple. However, the radius of curvature is not less than several thousand angstroms in the ordinary photoetching technique because the radius of curvature of the tip fully depends upon the accuracy of photolithography. Therefore, a microscope manufactured by this method is low in resolution. A maskless etching technique such as FIB (Focused Ion Beam) is required to make the radius of curvature smaller than the aforementioned size, but the manufacturing processes are complicated and the problem of cost occurs. In a stylus made with an etch pit of crystal employed as a mold, although the radius of curvature can be reduced to a comparatively small value, the manufacturing processes are complicated. Furthermore, since the adhesive properties between the stylus and the cantilever are poor, an observation in vibration mode is difficult.
The manufacturing method utilizing anisotropic etching is susceptible to various parameters during etching and is poor in reproducing a stylus configuration.